|“||God chose me to be tested, and now he's chosen them. If I don't do this, something terrible will happen ...||”|
— Clara to Hotch
When she was sixteen, the Hayes house burnt down, with Clara narrowly surviving the inferno. In an interview, her mother, Ellen Hayes, had called it a miracle, told the press that her daughter was tested by God and that she came through blessed. These events caused Clara, who was obsessive-compulsive, to become fixated on religion, fire and the number three (her house was number 333). Clara went on to get her own apartment (the walls of which she covered in religious texts relating to fire) in Tempe, Arizona and began attending Bradshaw College, but did poorly and was on the verge of flunking out, which was presumably her stressor.
In 2005, over the course of several months, Clara started several fires, which always corresponded to a convergence of threes (the first fire was started on March 3 at 3:00 p.m., for example). Eventually, on September 19, one of Clara's fires killed someone, a fellow college student named Matthew Rowland, whose death prompted the BAU to be called in. While the BAU is investigating the campus, Clara kills Professor Wallace, who is burned to death in his office when he turns on a lightbulb; Clara had rigged it to explode and ignite chemicals poured throughout the room. Hotch and Reid briefly meet Clara, when she and some of her classmates are telling them how they believe the unsub was starting the fires. Later, Clara, using a voice modifier, calls the campus tip line, leaving the cryptic message "Charon. I am doing this for Charon".
This message, coupled with Reid's deeper analysis of the crime scenes, causes the team to deduce that the unsub is an overly-religious obsessive-compulsive fixated on the number three. Hotch realizes that Clara is the unsub after remembering her behavior when he and Reid had spoken to her class (while describing how to make a Molotov cocktail, Clara raised three fingers, rotated her ring around her finger three times and repeating the word sugar, the third ingredient to the formula, three times). As the team began searching for Clara, she traps three of her classmates in an elevator on the third floor of the science building, dousing them with three bottles worth of chemicals when they manage to pull the door slightly open. Lighting a road flare, Clara is about to set her fellow students on fire with it when Hotch appears and tries to reason with her to buy enough time for backup to arrive. When Gideon reaches the scene, Hotch shoots Clara in the leg, causing her to drop the flare, which Gideon stops from rolling into the elevator. Clara is arrested and is either incarcerated or institutionalized afterwards.
"Wanna know how to make a Molotov cocktail that sets itself on fire? (counts the ingredients with her fingers) Potassium, sulfur... and normal sugar. Sugar. Sugar..."
The unsub (who was originally believed to be male, as most serial arsonists are) is a student, as serial arsonists are socially inept and teachers need high levels of confidence to stand up and teach classes. Unlike most serial arsonists, the unsub started fires not to watch them burn and gain a sense of power from them, but for other reasons entirely; the unsub was discovered to suffer from obsessive-compulsive disorder, specifically scrupulosity, which leaves obsessive fear of sin. When the unsub noticed trinities of three's, he would start a fire around whomever the pattern corresponded to, believing that person was chosen to be tested by God like the unsub believed he had been years earlier. The unsub is completely incapable of controlling himself and is convinced that if he did not test someone, a disaster of some kind would occur.
Clara targeted people in the college she went to, who she saw as having a trinity of threes in some aspects of their lives. Her first few fires and the one that killed Professor Wallace were started by what were essentially bombs: the victimless fires were started by road flares hooked up to timers, while the one that killed Wallace was started by a light bulb filled with fluids that caused a miniature explosion when the light was turned on, igniting other chemicals poured throughout the room. The fire that killed Matthew Rowland was started manually with chemicals that were poured under the door of his room, as well as the one Clara would have killed Jeremy and two other students, which involved her directly dousing them with chemicals. To stop the fires from being put out, Clara turned off the water in whatever building she intended to set ablaze.
- March 3: Unnamed victim (attempted; the fire failed to kill anyone)
- May 13: Unnamed victim (attempted; the fire failed to kill anyone)
- September 5: Unnamed victim (attempted; the fire failed to kill anyone)
- September 19:
- Two unnamed victims (attempted; the fires failed to kill anyone)
- Matthew Rowland (killed by a fire)
- September 28: Professor Ralph Wallace (killed by a homemade firebomb)
- September 29: Attempted to set the following on fire in an elevator she disabled:
- Two unnamed female students